Methods and apparatuses for testing one or more reception paths in a radar receiver

ABSTRACT

A method for testing at least one reception path in a radar receiver is provided. The reception path contains a mixer and a downstream signal processing circuit. The method involves injecting a test signal into the reception path, so that at least a first test tone having a frequency in a passband of the signal processing circuit and a second test tone having a frequency outside the passband are present on the reception path downstream of the mixer. Further, the method involves tapping off a baseband signal, generated by the signal processing circuit, from the reception path, the baseband signal being based on the test signal.

FIELD

Exemplary embodiments are concerned with checking the functionality ofradar receivers. In particular, exemplary embodiments are concerned withmethods and apparatuses for testing one or more reception paths in aradar receiver.

BACKGROUND

The behavior and/or configuration of single or multiple reception chainsof a radar receiver can be of interest or require monitoring.

SUMMARY

There is therefore a need to provide a technology for monitoring radarreceivers.

The need can be covered by the subject matter of the patent claims.

A first exemplary embodiment relates to a method for testing at leastone reception path in a radar receiver. The reception path includes amixer and a downstream signal processing circuit. The method includesinjecting a test signal into the reception path, so that at least afirst test tone having a frequency in a passband of the signalprocessing circuit and a second test tone having a frequency outside thepassband are present on the reception path downstream of the mixer.Further, the method includes tapping off a baseband signal, generated bythe signal processing circuit, from the reception path, the basebandsignal being based on the test signal.

In some exemplary embodiments, the method further includes generatingthe test signal by mixing the first test tone and the second test tonewith an oscillation signal for the mixer. The injecting of the testsignal into the reception path in this case includes applying the testsignal to a signal input of the mixer.

According to some exemplary embodiments, the test signal includes thefirst test tone and the second test tone, wherein the injecting of thetest signal into the reception path is effected downstream of the mixer.

In some exemplary embodiments, the method further includes determining afirst characteristic of the baseband signal at the frequency of thefirst test tone and determining a second characteristic of the basebandsignal at the frequency of the second test tone. Furthermore, the methodthen includes determining a characteristic of the reception path basedon the first characteristic of the baseband signal and the secondcharacteristic of the baseband signal.

According to some exemplary embodiments, the test signal has adiscontinuous frequency spectrum, wherein a bandwidth of the first testtone is smaller than a bandwidth of the passband.

In some exemplary embodiments, the frequency of the second test tone ischosen such that a characteristic that can be expected for the basebandsignal at the frequency of the second test tone according to a transferfunction of the signal processing circuit is in a predetermined range.

According to some exemplary embodiments, the frequency of the secondtest tone corresponds to a prescribed cutoff frequency from which thereis provision to attenuate signal components in the baseband signal by apredetermined attenuation in comparison with the passband.

In some exemplary embodiments, the frequency of the first test tonecorresponds to an envisaged cutoff frequency of the passband.

A second exemplary embodiment relates to a method for testing at leasttwo reception paths in a radar receiver. The two reception paths in thiscase each include a mixer and a downstream signal processing circuit.The method includes respectively injecting a test signal into the tworeception paths, so that in each case at least a first test tone and asecond test tone having frequencies in a passband of the signalprocessing circuits are present on the two reception paths downstream ofthe respective mixer. Further, the method includes tapping off a firstbaseband signal, generated by its signal processing circuit, from one ofthe two reception paths, the first baseband signal being based on thetest signal. The method furthermore includes tapping off a secondbaseband signal, generated by its signal processing circuit, from theother of the two reception paths, the second baseband signal being basedon the test signal.

According to some exemplary embodiments, the first baseband signal andthe second baseband signal are tapped off at the same time. The methodin this case further includes determining a first phase of the basebandsignal at the frequency of the first test tone and a second phase of thefirst baseband signal at the frequency of the second test tone and alsodetermining a first phase of the second baseband signal at the frequencyof the first test tone and a second phase of the second baseband signalat the frequency of the second test tone. Also, the method includesdetermining a relative phase response between the two reception pathsbased on the first phase of the first baseband signal, the second phaseof the first baseband signal, the first phase of the second basebandsignal and the second phase of the second baseband signal.

In some exemplary embodiments, the method further includes determining afirst amplitude of the first baseband signal at the frequency of thefirst test tone and a second amplitude of the first baseband signal atthe frequency of the second test tone and also determining an absolutephase response of one of the two reception paths based on the firstamplitude of the first baseband signal and the second amplitude of thefirst baseband signal. Alternatively or additionally, the method caninclude determining a first amplitude of the second baseband signal atthe frequency of the first test tone and a second amplitude of thesecond baseband signal at the frequency of the second test tone and alsodetermining the absolute phase response of the other of the tworeception paths based on the first amplitude of the second basebandsignal and the second amplitude of the second baseband signal.

According to some exemplary embodiments, the method further includesdetermining a first amplitude of the first baseband signal at thefrequency of the first test tone and a second amplitude of the firstbaseband signal at the frequency of the second test tone and alsodetermining a first amplitude of the second baseband signal at thefrequency of the first test tone and a second amplitude of the secondbaseband signal at the frequency of the second test tone. Also, themethod then includes determining a relative amplitude balance betweenthe two reception paths based on the first amplitude of the firstbaseband signal, the second amplitude of the first baseband signal, thefirst amplitude of the second baseband signal and the second amplitudeof the second baseband signal.

In some exemplary embodiments, the test signal has a discontinuity inthe frequency spectrum between a first signal component, generating thefirst test tone, and a second signal component, generating the secondtest tone, of the test signal.

A third exemplary embodiment relates to an apparatus for testing atleast one reception path in a radar receiver. The reception path in thiscase includes a mixer and a downstream signal processing circuit. Theapparatus includes an injection circuit configured to inject a testsignal into the reception path, so that at least a first test tonehaving a frequency in a passband of the signal processing circuit and asecond test tone having a frequency outside the passband are present onthe reception path downstream of the mixer. Further, the apparatusincludes a tapping circuit configured to tap off a baseband signal,generated by the signal processing circuit, from the reception path, thebaseband signal being based on the test signal.

According to some exemplary embodiments, the apparatus further includesan evaluation circuit configured to determine a first characteristic ofthe baseband signal at the frequency of the first test tone and a secondcharacteristic of the baseband signal at the frequency of the secondtest tone. The evaluation circuit is furthermore configured to determinea characteristic of the reception path based on the first characteristicof the baseband signal and the second characteristic of the basebandsignal.

In some exemplary embodiments, the apparatus and the radar receiver arearranged on a common semiconductor chip.

A fourth exemplary embodiment relates to an apparatus for testing atleast two reception paths in a radar receiver. The two reception pathsin this case each include a mixer and a downstream signal processingcircuit. The apparatus includes an injection circuit configured toinject a respective test signal into the two reception paths, so that ineach case at least a first test tone and a second test tone havingfrequencies in a passband of the signal processing circuits are presenton the two reception paths downstream of the respective mixer. Further,the apparatus includes a tapping circuit configured to tap off a firstbaseband signal, generated by its signal processing circuit, from one ofthe two reception paths and a second baseband signal, generated by itssignal processing circuit, from the other of the two reception paths.The first baseband signal and the second baseband signal are each basedon the test signal.

According to some exemplary embodiments, the apparatus further includesan evaluation circuit configured to determine a first phase of the firstbaseband signal at the frequency of the first test tone and a secondphase of the first baseband signal at the frequency of the second testtone. Further, the evaluation circuit is configured to determine a firstphase of the second baseband signal at the frequency of the first testtone and a second phase of the second baseband signal at the frequencyof the second test tone. The evaluation circuit is furthermoreconfigured to determine a relative phase response between the tworeception paths based on the first phase of the first baseband signal,the second phase of the first baseband signal, the first phase of thesecond baseband signal and the second phase of the second basebandsignal.

In some exemplary embodiments, the apparatus further includes anevaluation circuit configured to determine a first amplitude of thefirst baseband signal at the frequency of the first test tone and asecond amplitude of the first baseband signal at the frequency of thesecond test tone. Further, the evaluation circuit is configured todetermine a first amplitude of the second baseband signal at thefrequency of the first test tone and a second amplitude of the secondbaseband signal at the frequency of the second test tone. The evaluationcircuit is furthermore configured to determine a relative amplitudebalance between the two reception paths based on the first amplitude ofthe first baseband signal, the second amplitude of the first basebandsignal, the first amplitude of the second baseband signal and the secondamplitude of the second baseband signal.

According to some exemplary embodiments, the apparatus and the radarreceiver are arranged on a common semiconductor chip.

BRIEF DESCRIPTION OF THE DRAWINGS

Some examples of apparatuses and/or methods are explained in more detailbelow merely by way of example with reference to the accompanyingfigures, in which:

FIG. 1 shows a flowchart for an exemplary embodiment of a method fortesting at least one reception path in a radar receiver;

FIG. 2 shows a flowchart for an exemplary embodiment of a method fortesting at least two reception paths in a radar receiver;

FIG. 3 shows an exemplary embodiment of a transfer function for areception path; and

FIGS. 4-1 and 4-2 show an exemplary embodiment of an apparatus fortesting one or more reception paths in a radar receiver.

DETAILED DESCRIPTION

Various examples are now described in greater detail with reference tothe accompanying figures, which depict some examples. The thicknesses oflines, layers and/or areas in the figures may be exaggerated forclarity.

While further examples are suitable for various modifications andalternative forms, a few particular examples thereof are accordinglyshown in the figures and are described in detail below. However, thisdetailed description does not restrict further examples to theparticular forms described. Further examples can cover allmodifications, counterparts and alternatives that fall within the scopeof the disclosure. Identical reference signs refer throughout thedescription of the figures to identical or similar elements that can beimplemented identically or in modified form in comparison with oneanother, while they provide the same or a similar function.

It is to be noted that if one element is referred to as “connected” or“coupled” to another element, the elements can be connected or coupleddirectly or via one or more intermediate elements. If two elements A andB are combined using an “or”, this should be understood such that allpossible combinations are disclosed, i.e. only A, only B, and A and B.An alternative wording for the same combinations is “at least one of Aand B”. The same applies to combinations of more than two elements.

The terminology used here to describe specific examples is not intendedto have a limiting effect for further examples. When a singular form,e.g. “a, an” and “the”, is used and the use of only a single element isdefined neither explicitly nor implicitly as mandatory, further examplescan also use plural elements in order to implement the same function. Ifa function is described below as implemented using a plurality ofelements, further examples can implement the same function using asingle element or a single processing entity. Furthermore, it goeswithout saying that the terms “comprises”, “comprising”, “has” and/or“having” in their usage specify the presence of the indicated features,integers, steps, operations, processes, elements, components and/or agroup thereof, but do not exclude the presence or addition of one ormore other features, integers, steps, operations, processes, elements,components and/or a group thereof.

Unless defined otherwise, all terms (including technical and scientificterms) are used here in their customary meaning in the field with whichexamples are associated.

FIG. 1 shows a flowchart for a method 100 for testing at least onereception path in a radar receiver.

The radar receiver is a receiver configured to receive radar signals. Byway of example, the radar receiver can be configured to receive radarsignals with a wavelength in the millimeter range (e.g. FMCW (FrequencyModulated Continuous Wave) radar signals having a frequency in a bandfrom 76 to 81 GHz). The radar receiver can have one or more receptionpaths in order to down-convert one or more radio-frequency radar signalsto baseband and process them further. To this end, the at least onereception path comprises a mixer and a downstream signal processingcircuit. The mixer is designed to down-convert an appliedradio-frequency signal to baseband by means of an oscillation signal.The downstream signal processing circuit is configured to process thesignal output by the mixer further in the baseband frequency range. Byway of example, the signal processing circuit can comprise one or moreanalog filters, one or more analog-to-digital converters (ADC), one ormore digital filters, one or more decimation filters, one or moreamplifiers, etc. Method 100 can enable the behavior or configuration ofsingle or multiple instances of these assemblies to be tested.

To this end, method 100 comprises injecting 102 a test signal into thereception path, so that at least a first test tone (e.g. a firstsinusoidal tone) having a frequency in a baseband passband of the signalprocessing circuit and a second test tone (e.g. a second sinusoidaltone) having a frequency outside the baseband passband are present onthe reception path downstream of the mixer.

The first test tone and the second test tone are each tones having apredetermined, discrete frequency or predetermined, finite bandwidths.In other words: the first test tone and the second test tone areindividual test tones that are separate or distinguishable from oneanother in the frequency spectrum. That is to say that the signalpresent on the reception path, which signal comprises the first testtone and the second test tone, has a discontinuity in the frequencyspectrum between the first test tone and the second test tone. Adiscontinuity in the frequency spectrum of a signal is understood in thepresent application to be a range of the frequency spectrum thatcomprises one or more frequencies and in which the amplitude of thesignal is substantially zero (but e.g. can still contain signal noise).Accordingly, the test signal has a discontinuity in the frequencyspectrum between a first signal component, producing the first testtone, and a second signal component, producing the second test tone, ofthe test signal. The test signal therefore has a discontinuous frequencyspectrum. Besides the first test tone and the second test tone, it isalso possible for further discrete test tones to be applied to thereception path by the test signal.

The passband of the signal processing circuit is that frequency rangewithin which the signal processing circuit allows the frequenciescontained in an electrical signal to pass. The passband can beunderstood to be e.g. the frequency range in which the signal processingcircuit attenuates the frequencies contained in an electrical signal byless than a prescribed value (e.g. 3 decibels). The passband is adjoinedby a transition region that separates the passband from a stop band ofthe signal processing circuit. The stop band is that frequency range inwhich there is provision for frequencies contained in an electricalsignal to be attenuated by a predetermined attenuation in comparisonwith the passband. The first test tone is within the passband, while thesecond test tone is outside the passband, i.e. is in the transitionregion or in the stop band of the signal processing circuit. Thebandwidth of the first test tone is in this case smaller than thebandwidth of the passband based on the explanations above.

According to exemplary embodiments, method 100 can comprise generating106 the test signal beforehand. By way of example, the test signal canbe generated 106 by mixing the first test tone and the second test tonewith an oscillation signal for the mixer in order to generate a testsignal in the radar frequency range (e.g. in the range of 77 GHz) basedon the first and the second test tone. Accordingly, the injecting 102 ofthe test signal into the reception path then comprises applying the testsignal to a signal input of the mixer. The test signal is thereforegenerated such that the frequency of the oscillation signal used fordown-conversion differs from the frequency or the frequencies of thetest signal by the frequency of the respective test tones. For example,the following can apply: f_(osc)=f_(test)−f_(ton), where f_(osc)corresponds to the frequency of the oscillation signal, f_(test)corresponds to a respective frequency of the test signal and f_(ton)corresponds to the frequency of the respective test tone.

Alternatively, the generating 106 of the test signal can comprise mixingor combining two oscillation signals (e.g. two oscillation signalshaving frequencies in the gigahertz range). Similarly, the test signalcan be generated 106 such that the test signal comprises the first testtone and the second test tone, i.e. e.g. at frequencies in baseband thatare much lower than the radar frequency ranges. The test signal is thenaccordingly injected into the reception path downstream of the mixer.

Further, method 100 comprises tapping 104 a baseband signal generated bythe signal processing circuit from the reception path, the basebandsignal being based on the test signal. The tapped-off baseband signalcan now be used to determine one or more characteristics of thereception path on the basis of the first and second test tones. Thebaseband signal can in this case be tapped off at any point in thereception path downstream of the mixer. The location at which thebaseband signal is tapped off within the reception path can be chosen onthe basis of the assembly (assemblies) of the reception path that is/areto be tested, for example. The baseband signal can be tapped off e.g.via a memory (e.g. a random access memory, RAM) that is coupled to thereception path and that stores the baseband signal.

Method 100 can further comprise determining 108 a first characteristicof the baseband signal at the frequency of the first test tone anddetermining 110 a second characteristic of the baseband signal at thefrequency of the second test tone, for example. The first and the secondcharacteristic of the baseband signal are the value of a variablecharacterizing or describing the baseband signal at the frequency of therespective test tone. By way of example, the first and/or the secondcharacteristic can be an amplitude or a phase of the baseband signal atthe frequency of the respective test tone. The determination of thecharacteristic of the baseband signal at the frequency of the test tonescan comprise a Fourier analysis (e.g. a fast Fourier transformation—FastFourier Transform, FFT) of the baseband signal, for example. Method 100can accordingly furthermore comprise determining a characteristic of thereception path based on the first characteristic of the baseband signaland the second characteristic of the baseband signal. The characteristicof the reception path is a property characterizing or describing thebehavior of the reception path. By way of example, the firstcharacteristic of the baseband signal and the second characteristic ofthe baseband signal can be taken as a basis for determining whether thereception path exhibits a desired or selected behavior or a selectedconfiguration or a product requirement is observed.

Some exemplary characteristics of the reception path are explained inmore detail below with reference to FIG. 3 . . . 3 shows an exemplarytransfer function 310 for a signal processing circuit in the range from0 MHz to 25 MHz, indicating the expected amplitude profile of thebaseband signal over the depicted frequency range. Further, actual (e.g.measured) amplitudes 311, . . . , 315 of the baseband signal aredepicted in FIG. 3 for five test tones f1 to f5 applied to the receptionpath.

In the example shown in FIG. 3, it is assumed that the signal processingcircuit comprises an analog high-pass filter, an analog low-pass filter,a digital low-pass filter and a decimation filter. However, it should beborne in mind that this configuration is chosen for purely pedagogicreasons and method 100 is not restricted to this specific signalprocessing circuit.

The test tone f1 is in the frequency range attenuated by the analoghigh-pass filter. The test tone f2 is in the passband of the signalprocessing circuit above the attenuated frequency range of the analoghigh-pass filter. The test tone f3 is at a boundary of the passband ofthe digital low-pass filter (and therefore of the passband of the signalprocessing circuit). The test tone f4 is at a boundary of the stop bandof the digital low-pass filter (and therefore the stop band of thesignal processing circuit). The test tone f5 is in the stop band of thesignal processing circuit with a higher attenuation by the analoglow-pass filter.

The evaluation of the actual amplitudes 311, . . . , 315 of the basebandsignal after passing through the reception path at the frequencies ofthe test tones f1 to f5 allows characterization of the reception path.In this case, it is optionally also possible for the actual amplitudes311, . . . , 315 to be normalized in respect of configured expectations(e.g. reception gain).

If e.g. the test tone f2 is chosen as a first test tone within thepassband and the test tone f1 is chosen as a second test tone outsidethe passband of the signal processing circuit, it is possible to testwhether the analog high-pass filter of the signal processing circuit isoperating correctly. If the actual amplitude 311 of the baseband signalat the frequency of the second test tone f1 is attenuated in the rangeindicated by the transfer function 310 in FIG. 3, and if the actualamplitude 312 of the baseband signal at the frequency of the first testtone f2 is unattenuated, as indicated by the transfer function 310 inFIG. 3, it is possible to infer correct operation of the analog highpass filter. If the actual amplitude 311 of the baseband signal at thefrequency of the second test tone f1 were unattenuated, for example, itwould be possible to infer a malfunction in the analog high pass filterof the signal processing circuit.

If e.g. the test tone f3 is chosen as a first test tone within thepassband and the test tone f4 is chosen as a second test tone outsidethe passband of the signal processing circuit, it is possible to testwhether the digital low-pass filter is working correctly. If the actualamplitude 314 of the baseband signal at the frequency of the second testtone f4 is attenuated in the range indicated by the transfer function310 in FIG. 3, and if the actual amplitude 313 of the baseband signal atthe frequency of the first test tone f3 is unattenuated, as indicated bythe transfer function 310 in FIG. 3, it is possible to infer correctoperation of the digital low-pass filter. If an or the two actualamplitude(s) is/are not concordant with the transfer function 310, it ispossible to infer a malfunction in the digital low-pass filter.

In the example above with the test tones f3 and f4, the frequency of thesecond test tone f4 corresponds to a prescribed cutoff frequency fromwhich there is provision to attenuate signal components in the basebandsignal by a predetermined attenuation in comparison with the passband,since the test tone f4 is at the boundary of the stop band of thedigital low-pass filter. Also, the frequency of the first test tone f3corresponds to the envisaged cutoff frequency of the passband. The testtones f3 and f4 can therefore be used to test whether the passband ofthe signal processing circuit ends at the envisaged cutoff frequency andthe stop band of the signal processing circuit begins at the envisagedcutoff frequency.

The test tone f5 can e.g. furthermore be used to test whether theexpected joint attenuation of the analog low-pass filter and the digitallow-pass filter is observed. If the actual amplitude 315 of the basebandsignal at the frequency of the test tone f5 is in the range indicated bythe transfer function 310 in FIG. 3, it is possible to infer correctsetting or operation of the analog low-pass filter.

For the test on the signal processing circuit by means of test tonesoutside the passband of the signal processing circuit, it is alsoadvantageous to ensure that a characteristic to be measured (e.g.amplitude, phase) at the frequency used in the baseband signal of thesignal processing circuit is also measurable or is in a range suitablefor analyzing the characteristic. The frequency of the second test tonecan thus e.g. be chosen such that a characteristic that can be expectedfor the baseband signal at the frequency of the second test tone basedon a transfer function of the signal processing circuit is in apredetermined range. By way of example, the frequency of the second testtone can be chosen such that an amplitude of the baseband signal at thefrequency of the second test tone is in a predetermined range (e.g.above a measurability limit).

The first test tone and the second test tone (and optionally alsofurther test tones) can be injected at the same time, for example, andevaluated after a single measurement (for example by means of asubsequent FFT analysis). Alternatively, the reception path can also betested using individual (i.e. single, chronologically successive) testtones and by means of multiple measurements.

Method 100 can therefore allow a test on one or more reception paths ofa radar receiver using a small set of injected test tones.

A flowchart for a method 200 for testing at least two reception paths ina radar receiver is shown in FIG. 2. The two reception paths furthermoreeach comprise a mixer and a downstream signal processing circuit.

Method 200 comprises respectively injecting 202 a test signal into thetwo reception paths, so that in each case at least a first test tone anda second test tone having frequencies in a passband of the signalprocessing circuits are present on the two reception paths downstream ofthe respective mixer. The method 202 therefore involves in each case twotest tones being applied to the two reception paths, which are both inthe passband of the signal processing circuits. In this case, it isassumed that the signal processing circuits have substantially the samepassband.

Analogously to the principles described above for method 100, method 200can also comprise generating 208 the test signal beforehand. The testsignal in this case again has a discontinuity in the frequency spectrumbetween a first signal component, producing the first test tone, and asecond signal component, producing the second test tone, of the testsignal. Accordingly, the first test tone and the second test tone areagain individual test tones that are separated or distinguishable fromone another in the frequency spectrum. That is to say that therespective signals present on the reception paths, which signalscomprise the first test tone and the second test tone, each have adiscontinuity in the frequency spectrum between the first test tone andthe second test tone.

Method 200 furthermore comprises tapping off 204 a first baseband signalgenerated by its signal processing circuit from one of the two receptionpaths. The first baseband signal in this case is based on the testsignal. Further, method 200 comprises tapping off 206 a second basebandsignal generated by its signal processing circuit from the other of thetwo reception paths. The second baseband signal is also based on thetest signal. The tapped-off baseband signals can now be used todetermine one or more characteristics of the individual reception pathsand one or more characteristics of the reception paths relative to oneanother on the basis of the first and second test tones. The basebandsignals can in this case again be tapped off 204 and 206 according tothe principles described for method 100.

By way of example, the first baseband signal and the second basebandsignal can be tapped off at the same time. Method 200 can in this casefurther comprise determining 210 a first phase of the first basebandsignal at the frequency of the first test tone and a second phase of thefirst baseband signal at the frequency of the second test tone and alsodetermining 212 a first phase of the second baseband signal at thefrequency of the first test tone and a second phase of the secondbaseband signal at the frequency of the second test tone. Method 200 canthen further comprise determining 214 a relative phase response betweenthe two reception paths based on the first phase of the first basebandsignal, the second phase of the first baseband signal, the first phaseof the second baseband signal and the second phase of the secondbaseband signal.

Referring to the situation depicted in FIG. 3, it is possible e.g. forthe test tone f2 to be chosen as a first test tone and the test tone f2to be chosen as a second test tone. If the baseband signals of thereception paths are tapped off at the same time (e.g. recorded in aRAM), the relative phase response (relative phase difference) betweenthe reception paths can be monitored based on the difference between thephase values determined for each of the reception paths.

The test tones f2 and f3 can e.g. also be used to test a relativeamplitude balance between the two (or else further) reception paths.Method 200 then further comprises determining 216 a first amplitude ofthe first baseband signal at the frequency of the first test tone and asecond amplitude of the first baseband signal at the frequency of thesecond test tone and also determining 218 a first amplitude of thesecond baseband signal at the frequency of the first test tone and asecond amplitude of the second baseband signal at the frequency of thesecond test tone. Also, the method comprises determining 220 therelative amplitude balance between the two reception paths based on thefirst amplitude of the first baseband signal, the second amplitude ofthe first baseband signal, the first amplitude of the second basebandsignal and the second amplitude of the second baseband signal. Referringto the situation in FIG. 3, it is possible e.g. to determine theamplitudes of the baseband signal at the frequencies of the test tonesf2 and f3 for each reception path to be tested, in order to determinethe relative amplitude balance between the respective reception pathstherefrom. Method 200 can therefore be used to ensure that no receptionpath has deteriorated in comparison with the others.

In other words: the test tones in the passband can be used to determineor monitor relative characteristics between the respective receptionpaths.

The at least two test tones in the passband can alternatively be used todetermine characteristics of the individual reception paths themselves.

Method 200 can e.g. further comprise determining 222 a first amplitudeof the first baseband signal at the frequency of the first test tone anda second amplitude of the first baseband signal at the frequency of thesecond test tone and also determining 224 an absolute phase response ofone of the two reception paths based on the first amplitude of the firstbaseband signal and the second amplitude of the first baseband signal.Alternatively or additionally, method 200 can comprise determining 226 afirst amplitude of the second baseband signal at the frequency of thefirst test tone and a second amplitude of the second baseband signal atthe frequency of the second test tone and also determining 228 theabsolute phase response of the other of the two reception paths based onthe first amplitude of the second baseband signal and the secondamplitude of the second baseband signal. By way of example, it is tothis end again possible to use the test tones f2 and f3 shown in FIG. 3.

By comparing the actual amplitudes 312 and 313 of the baseband signalsat the frequencies of the test tones f2 and f3 with the transferfunction 310, it is e.g. also possible to test whether the two receptionpaths each achieve their selected or configured gain.

The actual amplitudes 312 and 313 of the baseband signals at thefrequencies of the test tones f2 and f3 can e.g. also be used todetermine the signal-to-noise ratio (SNR) of the individual channels. Inthe frequency spectrum of the respective baseband signals, only peakscan be expected for the test tones f2 and f3, and otherwise noise. Bycomparing the powers at the frequencies of the test tones f2 and f3 withthe noise power, it is possible to monitor the SNR and therefore e.g. totest whether a prescribed maximum SNR is exceeded or observed.

By testing the amplitudes of harmonics of the test tones f2 and f3, itis also possible to monitor linearity requirements on the receptionpaths.

Method 200 can therefore comprise determining a first characteristic ofthe first baseband signal at the frequency of the first test tone and asecond characteristic of the first baseband signal at the frequency ofthe second test tone and also determining a characteristic of one of thetwo reception paths based on the first characteristic of the firstbaseband signal and the second characteristic of the first basebandsignal. Alternatively or additionally, method 200 can comprisedetermining a first characteristic of the second baseband signal at thefrequency of the first test tone and a second characteristic of thesecond baseband signal at the frequency of the second test tone and alsodetermining a characteristic of the other of the two reception pathsbased on the first characteristic of the second baseband signal and thesecond characteristic of the second baseband signal.

Finally, FIGS. 4-1 and 4-2 show an exemplary embodiment of an apparatus400 for testing one or more reception paths of a radar receiver 440according to the principles shown in connection with methods 100 and200. Apparatus 400 and radar receiver 440 can be arranged e.g. on acommon semiconductor chip. Alternatively, apparatus 400 and radarreceiver 440 can also be arranged on different semiconductor chipsintended to detect objects during regular radar operation.

The exemplary radar receiver 440 depicted in FIGS. 4-1 and 4-2 comprisesfour reception paths that down-convert radar signals provided by asignal source 441 (e.g. one or more reception antennas for radarsignals) during normal operation to baseband in parallel and processthem further. In this case, it should be borne in mind that radarreceiver 400 can also comprise any other number of reception paths (e.g.one reception path or eight reception paths).

Each of the reception paths comprises a mixer 450 in order todown-convert radio-frequency signals that are present to baseband bymeans of an oscillation signal 401 (e.g. provided by a phase lockedloop, PLL). Further, each of the reception paths comprises a signalprocessing circuit 460 connected downstream of the mixer. The exemplarysignal processing circuit 460 depicted in FIGS. 4-1 and 4-2 comprises ananalog front end 461 (e.g. one or more analog filters), an ADC 462, adigital front end 463 (e.g. one or more digital filters), a digitalinterface 464 (e.g. a low voltage differential signaling (LVDSinterface) and a signal output 465. In this case, it should be borne inmind that signal processing circuit 460 can also comprise any otherconfiguration with other, fewer or more assemblies.

Apparatus 400 comprises an injection circuit 410 configured to inject atest signal 411 into one or more of the reception paths.

If the aim is for the radar receiver 440 to be tested e.g. according tomethod 100, injection circuit 410 is configured to inject the testsignal 411 into at least one reception path, so that at least a firsttest tone having a frequency in a passband of the signal processingcircuit 460 and a second test tone having a frequency outside thepassband are present on the reception path downstream of the mixer 450.

If the aim is for the radar receiver 440 to be tested e.g. according tomethod 200, injection circuit 410 is configured to inject in each casethe test signal 411 into at least two of the reception paths, so that ineach case at least a first test tone and a second test tone havingfrequencies in a passband of the signal processing circuits 460 arepresent on the two reception paths downstream of the respective mixer450.

As indicated in FIGS. 4-1 and 4-2, the injection circuit 410 can beconfigured to generate test signal 411 by mixing a signal 471 containingthe first test tone and the second test tone with the oscillation signal401 for the mixer 450. The test tones can be e.g. sinusoidal tones thatare output by a test tone generator 470. Accordingly, the injectioncircuit 410 is configured to inject the test signal 411 into thereception path 440 by applying the test signal 411 to a signal input ofthe mixer 450. Alternatively, the injection circuit 410 can e.g. also beconfigured to generate the test signal such that it comprises the firsttest tone and the second test tone. Accordingly, the injection circuit410 can then be configured to inject the test signal into the receptionpath 440 downstream of the mixer 450. In other words: the test signalcan be either a radio-frequency signal or a baseband signal.

Apparatus 400 also comprises a tapping-off circuit 420 configured to tapoff a baseband signal 451 generated by the respective signal processingcircuit from one or more of the reception paths.

If the aim is for the radar receiver 440 to be tested e.g. according tomethod 100, tapping-off circuit 420 is configured to tap off thebaseband signal 451 generated by the signal processing circuit 460 inone of the reception paths from the reception path. The baseband signal451 is based on the test signal 411 injected into the reception path.

If the aim is for the radar receiver 440 to be tested e.g. according tomethod 200, tapping-off circuit 420 is configured to tap off a firstbaseband signal generated by its signal processing circuit 460 from oneof the at least two reception paths and to tap off a second basebandsignal generated by its signal processing circuit 460 from the other ofthe at least two reception paths. The first baseband signal and thesecond baseband signal are each based on test signal 411.

The tapping-off circuit 420 can be e.g. in the form of a memory (e.g.RAM) that is coupled to one or more of the reception paths and in whichthe baseband signals of the respective reception paths are stored (e.g.streamed). By way of example, the baseband signals of the respectivereception paths can be stored simultaneously. Each of the storedbaseband signals can be stored e.g. with an accuracy of N=256 points.

Further, the apparatus 400 comprises an evaluation circuit 430 thattakes the one or more tapped-off baseband signals as a basis fordetermining characteristics of the individual reception paths orcharacteristics between the individual reception paths. As indicated inFIGS. 4-1 and 4-2, the evaluation circuit 430 can be configured tooutput a particular characteristic to a monitoring output 480 of theapparatus 400. By way of example, the evaluation circuit 430 can beconfigured to output an error signal or a signal indicating correctoperation to the monitoring output 480.

In order to be able to perform spectral analysis for the tapped-offbaseband signals, the evaluation circuit 430 can comprise e.g. a Fouriertransformation circuit 431 (e.g. for an FFT) that is configured todetermine a frequency spectrum of the respective baseband signal. Therecordings of the baseband signals can therefore have spectral analysisperformed for them—e.g. by rating the amplitude and phase of multipledefined FFT coefficients. To this end, the evaluation circuit 430 cane.g. furthermore have a processing circuit 432 on which a COordinateRotation Digital Computer (CORDIC) algorithm runs. Both the Fouriertransformation and the CORDIC algorithm can in this case be implementedas a piece of software running on a processor or as a dedicated circuit.The Fourier transformation circuit 431 or the processing circuit 432 canbe part of the reception chain of the radar receiver, i.e. the Fouriertransformation circuit 431 used for evaluating the test signal is usedduring regular operation, e.g. in order to produce a range-Doppler mapfor detecting objects. The use of discrete test tones in basebandtherefore results in the synergistic advantage that the existing Fouriertransformation circuit 431 of the radar receiver can be used foranalyzing the discrete test tones, since these show themselves asdiscrete peaks after the Fourier transformation. The monitoring, i.e.the supply of the test signals, can be effected intermittently with thegeneration of regular radar signals for object detection. In otherwords: the supply between two measurements can achieve completemonitoring of the reception chain during regular radar operation.

An error handling circuit (error handler) 433 can be used to determinedifferences from prescribed configurations or failures of individualmultiple assemblies in the reception paths. Error handling circuit 433can e.g. output an error signal or a signal indicating correct operationto the monitoring output 480.

In respect of the analysis of the tapped-off baseband signals, referenceshould be made merely by way of example to some of the aspects alreadydiscussed in connection with the methods 100 and 200. It goes withoutsaying that the evaluation circuit 430 can determine not only theanalyses cited below but also further characteristics.

In line with method 100, evaluation circuit 430 can be configured forexample to determine a first characteristic of the baseband signal 451at the frequency of the first test tone and to determine a secondcharacteristic of the baseband signal 451 at the frequency of the secondtest tone. Based on the first characteristic of the baseband signal andthe second characteristic of the baseband signal, the evaluation circuit430 can further be configured to determine a characteristic of thereception path.

In line with method 200, evaluation circuit 430 can be configured forexample to determine a first phase of a first baseband signal (of afirst reception path) at the frequency of the first test tone and asecond phase of the first baseband signal at the frequency of the secondtest tone and to determine a first phase of a second baseband signal (ofa second reception path) at the frequency of the first test tone and asecond phase of the second baseband signal at the frequency of thesecond test tone. Based on the first phase of the first baseband signal,the second phase of the first baseband signal, the first phase of thesecond baseband signal and the second phase of the second basebandsignal, the evaluation circuit 430 can further be configured todetermine a relative phase response between the two reception paths.

Alternatively, in line with method 200, evaluation circuit 430 can beconfigured for example to determine a first amplitude of a firstbaseband signal (of a first reception path) at the frequency of thefirst test tone and a second amplitude of the first baseband signal atthe frequency of the second test tone and to determine a first amplitudeof a second baseband signal (of a second reception path) at thefrequency of the first test tone and a second amplitude of the secondbaseband signal at the frequency of the second test tone. Based on thefirst amplitude of the first baseband signal, the second amplitude ofthe first baseband signal, the first amplitude of the second basebandsignal and the second amplitude of the second baseband signal, theevaluation circuit 430 can further be configured to determine a relativeamplitude balance between the two reception paths.

The monitoring quality can be dependent on the number of spectral pointsto be evaluated. As the description above has shown, some test tones cansuffice for achieving monitoring aims for one or more reception paths ofa radar receiver. According to the principles set out above, the testtones can e.g. all be injected at the same time and evaluated after asingle measurement, or individual test tones evaluated in multiplemeasurements can be injected.

As the discussion above has shown, the proposed technique can be usede.g. to test the correct application of a configured gain in a receptionpath or of filter corner frequencies. Similarly, e.g. quality parametershaving defined boundaries can be tested. Purely by way of example,reference should be made in this case to the SNR, the relative phasedifference between reception paths, the relative amplitude balancebetween reception paths or the linearity of a reception path.

The proposed technique can be used to determine the receptioncharacteristics of a system by means of the production of a minimum setof test tones. In other words: the proposed technique can allow fast andefficient monitoring of reception paths, since radar systems are linearand time-invariant and errors do not increase the complexity (e.g. afilter order). The less it is necessary to actively monitor something ona chip, the less excess power/heat it is necessary to compensate for onthe chip by means of switched-off phases. It is therefore possible formore time to be used for active radar operation. The duty cycle of theradar system can therefore be positively influenced by the proposedtechnique. On the basis of the fast and efficient monitoring, the dutycycle of the radar can be increased.

The proposed technique can therefore allow reception path monitoring bymeans of individual injected sideband test tones.

The aspects and features described together with one or more of theexamples and figures detailed above can also be combined with one ormore of the other examples in order to replace an identical feature ofthe other example or in order to introduce the feature into the otherexample additionally.

The description and drawings present only the principles of thedisclosure. Furthermore, all examples mentioned here are fundamentallyintended to be used expressly only for teaching purposes, in order toassist the reader in understanding the principles of the disclosure andthe concepts contributed by the inventor(s) for further development ofthe art. All statements herein regarding principles, aspects andexamples of the disclosure and also concrete examples thereof areintended to encompass the counterparts thereof.

It goes without saying that the disclosure of multiple steps, processes,operations or functions disclosed in the description or the claimsshould not be interpreted as being in a specific order, unlessexplicitly or implicitly indicated otherwise, e.g. for technicalreasons. The disclosure of multiple steps or functions thus does notlimit them to a specific order, unless said steps or functions are notinterchangeable for technical reasons. Further, in some examples, anindividual step, function, process or operation can include multiplesubsteps, subfunctions, subprocesses or suboperations and/or can besubdivided into them. Such substeps may be included and be part of thedisclosure of said individual step, provided that they are notexplicitly excluded.

Furthermore, the claims that follow are hereby incorporated in thedetailed description, where each claim may stand alone as a separateexample. While each claim may stand alone as a separate example, itshould be borne in mind that—although a dependent claim can refer in theclaims to a specific combination with one or more other claims—otherexamples can also encompass a combination of the dependent claim withthe subject matter of any other dependent or independent claim. Suchcombinations are explicitly proposed here, provided that no indicationis given that a specific combination is not intended. Furthermore,features of a claim are also intended to be included for any otherindependent claim, even if this claim is not made directly dependent onthe independent claim.

What is claimed is:
 1. A method for testing at least one reception pathin a radar receiver, wherein a reception path comprises a mixer and adownstream signal processing circuit, the method comprising: injecting atest signal into the reception path, so that at least a first test tonehaving a frequency in a passband of the downstream signal processingcircuit and a second test tone having a frequency outside the passbandare present on the reception path downstream of the mixer; tapping abaseband signal, generated by the downstream signal processing circuit,from the reception path, the baseband signal being based on the testsignal; determining a first characteristic of the baseband signal at thefrequency of the first test tone; determining a second characteristic ofthe baseband signal at the frequency of the second test tone; anddetermining a characteristic of the reception path based on the firstcharacteristic of the baseband signal and the second characteristic ofthe baseband signal.
 2. The method as claimed in claim 1, furthercomprising: generating the test signal for the mixer by mixing the firsttest tone and the second test tone with an oscillation signal, whereinthe injecting of the test signal into the reception path comprisesapplying the test signal to a signal input of the mixer.
 3. The methodas claimed in claim 1, wherein the test signal comprises the first testtone and the second test tone, and wherein the injecting of the testsignal into the reception path is effected downstream of the mixer. 4.The method as claimed in claim 1, wherein: the test signal has adiscontinuous frequency spectrum, and a bandwidth of the first test toneis smaller than a bandwidth of the passband.
 5. The method as claimed inclaim 1, wherein the frequency of the second test tone is chosen suchthat a characteristic that can be expected for the baseband signal atthe frequency of the second test tone according to a transfer functionof the downstream signal processing circuit is in a predetermined range.6. The method as claimed in claim 1, wherein the frequency of the secondtest tone corresponds to a prescribed cutoff frequency from which thereis provision to attenuate signal components in the baseband signal by apredetermined attenuation in comparison with the passband.
 7. The methodas claimed in claim 1, wherein the frequency of the first test tonecorresponds to an envisaged cutoff frequency of the passband.
 8. Amethod for testing at least two reception paths in a radar receiver,wherein the at least two reception paths each comprise a mixer and adownstream signal processing circuit, the method comprising:respectively injecting a test signal into the at least two receptionpaths, wherein the test signal comprises at least a first test tone anda second test tone having different frequencies in a passband of eachdownstream signal processing circuit, wherein the test signal isinjected into each of the at least two reception paths so that in eachcase the first test tone and the second test tone are present on each ofthe at least two reception paths downstream of a respective mixer;tapping a first baseband signal, generated by a first respectivedownstream signal processing circuit, from a first one of the at leasttwo reception paths, the first baseband signal being based on the testsignal; and tapping a second baseband signal, generated by a secondrespective downstream signal processing circuit, from a second one ofthe at least two reception paths, the second baseband signal being basedon the test signal, wherein the first baseband signal and the secondbaseband signal are tapped at a same time, and wherein the methodfurther comprises: determining a first phase of the first basebandsignal at a frequency of the first test tone and a second phase of thefirst baseband signal at a frequency of the second test tone;determining a first phase of the second baseband signal at the frequencyof the first test tone and a second phase of the second baseband signalat the frequency of the second test tone; and determining a relativephase response between the at least two reception paths based on thefirst phase of the first baseband signal, the second phase of the firstbaseband signal, the first phase of the second baseband signal, and thesecond phase of the second baseband signal.
 9. The method as claimed inclaim 8, wherein the test signal has a discontinuity in a frequencyspectrum between a first signal component that produces the first testtone of the test signal and a second signal component that produces thesecond test tone of the test signal.
 10. A method for testing at leasttwo reception paths in a radar receiver, wherein the at least tworeception paths each comprise a mixer and a downstream signal processingcircuit, the method comprising: respectively injecting a test signalinto the at least two reception paths, wherein the test signal comprisesat least a first test tone and a second test tone having differentfrequencies in a passband of each downstream signal processing circuit,wherein the test signal is injected into each of the at least tworeception paths so that in each case the first test tone and the secondtest tone are present on each of the at least two reception pathsdownstream of a respective mixer; tapping a first baseband signal,generated by a first respective downstream signal processing circuit,from a first one of the at least two reception paths, the first basebandsignal being based on the test signal; tapping a second baseband signal,generated by a second respective downstream signal processing circuit,from a second one of the at least two reception paths, the secondbaseband signal being based on the test signal; determining a firstamplitude of the first baseband signal at the frequency of the firsttest tone and a second amplitude of the first baseband signal at thefrequency of the second test tone; determining an absolute phaseresponse of the first one of the at least two reception paths based onthe first amplitude of the first baseband signal and the secondamplitude of the first baseband signal; determining a first amplitude ofthe second baseband signal at the frequency of the first test tone and asecond amplitude of the second baseband signal at the frequency of thesecond test tone; and determining the absolute phase response of thesecond one of the at least two reception paths based on the firstamplitude of the second baseband signal and the second amplitude of thesecond baseband signal.
 11. A method for testing at least two receptionpaths in a radar receiver, wherein the at least two reception paths eachcomprise a mixer and a downstream signal processing circuit, the methodcomprising: respectively injecting a test signal into the at least tworeception paths, wherein the test signal comprises at least a first testtone and a second test tone having different frequencies in a passbandof each downstream signal processing circuit, wherein the test signal isinjected into each of the at least two reception paths so that in eachcase the first test tone and the second test tone are present on each ofthe at least two reception paths downstream of a respective mixer;tapping a first baseband signal, generated by a first respectivedownstream signal processing circuit, from a first one of the at leasttwo reception paths, the first baseband signal being based on the testsignal; tapping a second baseband signal, generated by a secondrespective downstream signal processing circuit, from a second one ofthe at least two reception paths, the second baseband signal being basedon the test signal; determining a first amplitude of the first basebandsignal at the frequency of the first test tone and a second amplitude ofthe first baseband signal at the frequency of the second test tone;determining a first amplitude of the second baseband signal at thefrequency of the first test tone and a second amplitude of the secondbaseband signal at the frequency of the second test tone; anddetermining a relative amplitude balance between the at least tworeception paths based on the first amplitude of the first basebandsignal, the second amplitude of the first baseband signal, the firstamplitude of the second baseband signal, and the second amplitude of thesecond baseband signal.
 12. An apparatus for testing at least onereception path in a radar receiver, wherein a reception path comprises amixer and a downstream signal processing circuit, the apparatuscomprising: an injection circuit configured to inject a test signal intothe reception path, so that at least a first test tone having afrequency in a passband of the downstream signal processing circuit anda second test tone having a frequency outside the passband are presenton the reception path downstream of the mixer; a tapping circuitconfigured to tap a baseband signal, generated by the downstream signalprocessing circuit, from the reception path, the baseband signal beingbased on the test signal; further comprising an evaluation circuitconfigured to: determine a first characteristic of the baseband signalat the frequency of the first test tone; determine a secondcharacteristic of the baseband signal at the frequency of the secondtest tone; and determine a characteristic of the reception path based onthe first characteristic of the baseband signal of the secondcharacteristic of the baseband signal.
 13. The apparatus as claimed inclaim 12, wherein the apparatus and the radar receiver are arranged on acommon semiconductor chip.
 14. An apparatus for testing at least tworeception paths in a radar receiver, wherein the at least two receptionpaths each comprise a mixer and a downstream signal processing circuit,the apparatus comprising: an injection circuit configured to inject atest signal into the at least two reception paths, wherein the testsignal comprises at least a first test tone and a second test tonehaving different frequencies in a passband of each downstream signalprocessing circuit, wherein the test signal is injected into each of theat least two reception paths so that in each case the first test toneand the second test tone are present on each of the at least tworeception paths downstream of a respective mixer; a tapping circuitconfigured to tap a first baseband signal, generated by a firstrespective downstream signal processing circuit, from a first one of theat least two reception paths, and tap a second baseband signal,generated by a second respective downstream signal processing circuit,from a second one of the at least two reception paths, the firstbaseband signal and the second baseband signal each being based on thetest signal; and an evaluation circuit configured to: determine a firstphase of the first baseband signal at a frequency of the first test toneand a second phase of the first baseband signal at a frequency of thesecond test tone; determine a first phase of the second baseband signalat the frequency of the first test tone and a second phase of the secondbaseband signal at the frequency of the second test tone; and determinea relative phase response between the at least two reception paths basedon the first phase of the first baseband signal, the second phase of thefirst baseband signal, the first phase of the second baseband signal andthe second phase of the second baseband signal.
 15. The apparatus asclaimed in claim 14, wherein the apparatus and the radar receiver arearranged on a common semiconductor chip.
 16. An apparatus for testing atleast two reception paths in a radar receiver, wherein the at least tworeception paths each comprise a mixer and a downstream signal processingcircuit, the apparatus comprising: an injection circuit configured toinject a test signal into the at least two reception paths, wherein thetest signal comprises at least a first test tone and a second test tonehaving different frequencies in a passband of each downstream signalprocessing circuit, wherein the test signal is injected into each of theat least two reception paths so that in each case the first test toneand the second test tone are present on each of the at least tworeception paths downstream of a respective mixer; a tapping circuitconfigured to tap a first baseband signal, generated by a firstrespective downstream signal processing circuit, from a first one of theat least two reception paths, and tap a second baseband signal,generated by a second respective downstream signal processing circuit,from a second one of the at least two reception paths, the firstbaseband signal and the second baseband signal each being based on thetest signal; and an evaluation circuit configured to: determine a firstamplitude of the first baseband signal at the frequency of the firsttest tone and a second amplitude of the first baseband signal at thefrequency of the second test tone; determine a first amplitude of thesecond baseband signal at the frequency of the first test tone and asecond amplitude of the second baseband signal at the frequency of thesecond test tone; and determine a relative amplitude balance between theat least two reception paths based on the first amplitude of the firstbaseband signal, the second amplitude of the first baseband signal, thefirst amplitude of the second baseband signal and the second amplitudeof the second baseband signal.